Thanks folks. The sound stops when engine not running so maybe the cure is to not start the engine lol :-)
Seriously though, the chuffing is rpm related but at 25 mph (ish) it is easy to hear as the road noise isnt too loud.
It is very noticeable when running close to walls/building as the sound reflects back.
There is no obvious oil loss apart from a drip from primary chain case (cork seal leak).
Would anyone think it is a magdyno shimming related issue?
Ian
After further investigation and a fair degree of frustration, I took the dynamo off again, but this time I swopped it for one that I had recently refurbished (I've got 7 sitting here now!) and VOILLA!! The wierd chuffing has stopped doing it's thing!
What is odd is that the dynamo I took off was recently refurbished (not by me) and, when turned by hand it rotates freely on the bearings and makes no unusual noise...
Beats me!! I sometimes get the feeling my bloody bike has a ghost lurking in it somewhere!